a living organism characterized by voluntary movement

membranous duct connecting the fetus with the placenta

the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development.

early stage of an embryo produced by cleavage of an ovum; a liquid-filled sphere whose wall is composed of a single layer of cells; during this stage (about eight days after fertilization) implantation in the wall of the uterus occurs

double-walled stage of the embryo resulting from invagination of the blastula; the outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm

a solid mass of blastomeres that forms when the zygote splits; develops into the blastula

membranous duct connecting the fetus with the placenta